old steel frame

I just finished striping my old bike and building up my new frame. Its going to need many upgrades in the near future, but its good for now. This leaves me with an old steel frame that im debating what to do with. I have thought about just puting it back together as I upgrade the new bike and using it as a beater. But I was also toying with a couple other ideas.

Single speed perhaps? I still dont really know what the advantage to one is, but it sounds kind of cool.

Another idea was to get big tall handlebars, a big granny seat, and slicks, and turn it into an around the neighborhood leisurely rider.